The present invention relates to a semiconductor device used in microwave circuits or high-speed digital circuits, and, more specifically, to an improvement in a package for the semiconductor devices, suitable to cascade connection.
Solid-state microwave devices, such as GaAs-FETs (gallium arsenide Field Effect Transistors) have been used in wide-band amplifiers for communication equipment or a booster amplifier for a voltage-controlled oscillator operated in a microwave frequency band ranging from 2 GHz to 30 GHz or higher. In the band, packaging design for such a GaAs-FET must be performed on the basis of a concept different from transistors or ICs (Integrated Circuits) which are operated in the relatively low frequency bands, since the dimensions of the package become close to the wave length of a microwave signal. For instance, 3 cm for the wave length signal of 10 GHz.
The inventor has described packages for a semiconductor device used in 2 to 30 GHz band in co-pending U.S. application Ser. Nos. 571,542 and 708,609. The packages described in these applications, comprise a metallic container for a semiconductor device or circuit housed therein, which are intended to solve the problems occurring in prior art packages comprising a ceramic container at such a high frequency band. That is, the ceramic container has undesirable influences which become remarkable when the semiconductor device or circuit housed therein is operated at a microwave frequency band. For instance, a ring-shaped metallized layer formed on a ceramic container, which is for attaching a lid thereon, would function as a resonator, thereby establishing an apparent oscillation circuit in conjunction with the parasitic capacitance relating to the ceramic container. In a practical package, the oscillation frequency defined by the inductance of the ring-shaped metallized layer and the parasitic capacitance usually matches a microwave frequency in the band, therefore, the effective frequency band allowed for the semiconductor device or circuit is inevitably narrowed. Other kinds of problems relating to such a ceramic container have been described in the specifications of the above U.S. applications.
The package described above comprising a metallic container can be free from problems including the above-mentioned oscillation characteristic of the ceramic container. However, different problems arise from the insufficient positional accuracy of input/output terminals provided on a metallic package. In each package, the input/output terminal having a strip line is hermetically sealed to the metallic container in separated relationship such that each of the strip lines is electrically isolated from the metallic container. The terminals are apt to deviate from their respective designated positions on the metallic container during the hermetic sealing process. Poor positional accuracy of the terminals results in an unfavorable bonding between the packages in a cascade connection. Such unfavorable bonding includes, for example, the increase in the length of the bonding ribbons interconnecting, respectively, corresponding terminals on the cascaded packages, and a step involved between the strip line and the bonding ribbon. These structural failures in the bonding cause impedance mismatch and result in the degradation of high-frequency characteristics of the circuit comprising the packages. These problems in the above-described package will be further discussed later with reference to the related drawings herein.